The present invention relates generally to the field of printing, and more particularly to techniques for selectively removing portion(s) of a xe2x80x9cprinting blanketxe2x80x9d which is part of or used in conjunction with a printing machine.
Printing machines capable of producing high speed, high quality media, promotional literature, books, packaging and the like, are common. The present invention generally relates to high speed printing machines and processes, and more particularly to offset printing machines and processes.
An offset printing machine typically includes several drums or xe2x80x9ccylindersxe2x80x9d that are rotatably mounted on a framework, with the rotational axes of the cylinders substantially parallel to one another. The drive mechanisms for the cylinders are typically interconnected by gears, etc. so as to rotate the cylinders together. The paper, cardboard, etc. (occasionally referred to herein as the xe2x80x9csubstratexe2x80x9d) is automatically fed into the machine and processed by the various cylinders to produce the desired result.
One of the cylinders in a typical offset printing machine is the plate cylinder. It carries a metal plate that has been photographically etched or otherwise processed to reproduce the image of the text and/or graphics to be transferred to the substrate. As the plate cylinder rotates it is inked, and the image is transferred to a so-called blanket cylinder which in turn transfers the image to the substrate. The blanket cylinder carries a sheet-like xe2x80x9cblanket,xe2x80x9d oftentimes made of rubber or some other polymeric material, which accepts the image from the plate cylinder and presses the image onto the substrate. In addition, a typical offset printing machine will include a coater apparatus for applying any of a wide variety of coatings, e.g., waterproofing, to the substrate. When a job requires coating, the coater apparatus is shifted into direct contact with the blanket cylinder while the plate cylinder is not operable to transfer ink images to the rubber surface. As an alternative to this arrangement (wherein the blanket cylinder is part of the printing unit and is used just for coating while the plate cylinder is not in service), the blanket cylinder can be part of an inline coating unit constructed independently of the printing unit to provide inline coating reproduction. Given these alternative approaches, the terms xe2x80x9cblanketxe2x80x9d or xe2x80x9cprinting blanketxe2x80x9d are used below to refer to any blanket used in a printing machine, whether the blanket is arranged to interact with the plate cylinder, or whether the blanket is part of a separate inline coating unit.
On occasion, it is desired to use the coater to selectively coat only portions of the substrate. Or, it is sometimes desired to apply coating to most of the substrate, but to not coat certain select portions of the substrate, e.g., where an adhesive is to be applied, or where there are symbols or UPC codes that need to be scanned, or an area that includes mail metering information. When it is desired to not coat select portions of the substrate, the operator typically cuts out or relieves the blanket in those areas, so that the waterproofing (for example) is not applied in those select areas. Usually this is done after the blanket is installed on its cylinder, and historically the installed blanket is cut freehand with a small knife, e.g., an xe2x80x9cX-Actoxe2x80x9d knife. This freehand cutting technique is time consuming and often inaccurate, resulting in spoilage of the blanket.
The present invention addresses the blanket cutting problem discussed above, and presents a cost-effective method and apparatus for cutting a mounted printing blanket in a manner that is faster and more accurate than by freehand.
The apparatus of the present invention is a blanket cutter for cutting a printing blanket having a cylinder axis, including an elongated rail arranged substantially parallel to the cylinder axis and a blanket cutting device slidably engaged with the rail. An axial/horizontal blanket cut can be made by operatively engaging the printing blanket with the blanket cutting device and axially sliding the cutting device along the rail. A circumferential/vertical blanket cut can be made by operatively engaging the printing blanket with the blanket cutting device and effecting relative rotational movement, about the cylinder axis, between the printing blanket and the blanket cutting device.
In a preferred embodiment, the printing blanket is rotationally supported by a framework, and the elongated rail is a separate structure which is secured to the framework. Also, preferably, a circumferential/vertical blanket cut can be made by rotating the printing blanket relative to a rotationally stationary blanket cutting device.
In addition, the elongated rail can form a slot which slidably receives the blanket cutting device, wherein the rail is metal and at least a portion of the blanket cutting device is plastic, to reduce friction. Preferably the rail slot and the plastic portion of the blanket cutting device are xe2x80x9cT-shapedxe2x80x9d to eliminate unwanted motion therebetween but freely permit axial sliding motion of the blanket cutting device on the rail.
Also, a preferred blanket cutting device can include a knife having a blade that makes physical contact with the printing blanket to make the cuts. The knife can be rotated or twisted about its axis to change the blade orientation depending on whether a circumferential or axial blanket cut is desired. A threaded adjustment knob can selectively engage the knife to lock it in place in the desired orientation.
Since the depth of the blanket cut is often critical, a preferred apparatus according the present invention includes an adjustable collar that attaches to the tail end of the knife to act as a xe2x80x9cstop,xe2x80x9d so that the depth of cut will not change as the knife is rotated when the cut direction is changed, for example.
The method of the present invention broadly includes the steps of selecting an elongated rail, positioning the rail parallel to the printing blanket cylinder axis, selecting a blanket cutting device, operatively engaging the printing blanket with the blanket cutting device, axially sliding the blanket cutting device along the rail to axially cut the blanket, and effecting relative rotational movement between the printing blanket and the blanket cutting device to circumferentially cut the blanket.
In a preferred method, the step of effecting relative movement between the printing blanket and the blanket cutting device includes rotating the printing blanket about the cylinder axis.
In another preferred method, the step of selecting the elongated rail includes selecting a structure that is separate from the framework or catwalk; and the step of positioning the rail comprises attaching the rail to the framework.
A preferred method is also characterized in that the blanket cutting device includes a knife blade, and the step of operatively engaging the printing blanket with the blanket cutting device includes placing the knife blade into physical contact with the blanket.
Finally, in preferred printing blanket methods according to the present invention the rail forms a slot and the blanket cutting device includes an extending element that fits within and conforms to the slot; and wherein the slot and extending element are T-shaped.